Natural gas production through hydraulic fracturing of shale formations is a rapidly accelerating field. Shale gas is now widely viewed in the U.S. as a key asset, which can bolster a more energy-independent future. In the midst of widespread optimism towards shale gas, certain environmental concerns have arisen that center on seismic effects of hydraulic fracturing as well as the aggressive consumption of water and, more importantly, possible pollution of local water resources by produced and flowback waters.
Frac/Produced water is the largest waste stream generated in the gas industry. It is a mixture of different organic and inorganic compounds. Due to the increasing volume requirements of water, the outcome and effect of discharging frac/produced water on the environment has become an increasingly significant issue of environmental concern. Many environmental activists worry that fracking fluids and produced water could contaminate nearby groundwater.
Even though fracking chemicals make up approximately 0.5% of the overall drilling fluids, this proportion still amounts to some 25,000 gal. (95,000 L) in a well with 5 million-gallons (19 million L) of water. Even in an ideal case, hydraulic fracturing can produce over 1 million gal. (3.8 million liters) of toxic, briny wastewater over the lifetime of an individual well. In western states like Texas, companies can store the wastewater in deep underground control wells, but in eastern states like Pennsylvania, geology makes that difficult. As a result, drillers have had to ship much of their wastewater to nearby municipal treatment plants by truck. Hence, the transportation of the frac/produced water itself becomes another environmental concern with additional burden to develop improved roadways for trucks.
Frac/produced water is conventionally treated using a range of physical, chemical, and biological methods. Since there are multiple needs that should be addressed in produced water treatment, a variety of different conventional methodologies have been used, including the following: activated carbon, various forms of filtration (such as sand filters, cartridge filters, multi-media filtration, membrane filtration), organic-clay adsorbers, chemical oxidation, UV disinfection, chemical biocides, air strippers, chemical precipitation, water-softening by the application of lime soda, clarifiers, settling ponds, ion exchange, reverse osmosis, evaporation, steam stripping, and acidification. In nearly all of the above cases, each modality of technology typically addresses only a single treatment target. For example, UV disinfection can only destroy bacteria and is unable to address any of the other objectives. Other processes that are potentially applicable to produced water treatment can be applied to only a limited number of basic functions.
The present invention is directed to surmounting some of these problems.